JP7507394B2 - Laser Processing Head - Google Patents

Description

The present invention relates to a laser processing head.

It has been known for some time that a high-power laser beam can heat and distort the optical elements in the processing head, causing a thermal lens effect and resulting in a change in the focal position (see, for example, Patent Document 1).

Patent Document 1 discloses a configuration that includes first and second optical members having a wedge surface and a flat surface, with the wedge surfaces of the first and second optical members arranged to face each other, and the first and second optical members moved relatively parallel to the flat surface. This adjusts the ratio of the thicknesses of the first and second optical members through which the light beam passes, thereby compensating for the thermal lens effect.

Patent No. 5099599

However, the invention of Patent Document 1 requires the formation of wedge surfaces on the first and second optical members, which increases the cost of processing the parts.

The present invention was made in consideration of these points, and its purpose is to suppress fluctuations in the focusing position caused by the thermal lens effect with a relatively simple configuration.

A first invention is a laser processing head that outputs laser light incident from a transmission fiber to a workpiece, the laser processing head including a plurality of optical members arranged on the output side of the transmission fiber and aligned along an optical axis direction, the plurality of optical members including a first optical member formed of a material having a positive refractive index temperature coefficient and a second optical member formed of a material having a negative refractive index temperature coefficient, the second optical member having flat surfaces on both sides,
The optical element is characterized in that the identification number i of the optical element, the light absorptance p _i of the optical element, the refractive index temperature coefficient Δn _i of the optical element, the thickness t _i of the optical element, the focusing radius R _i of the laser light on the surface of the optical element, and the focusing position fluctuation Δd satisfy the conditions Δd∝p ₁ ×Δn ₁ ×t ₁ /R ₁ ² + ... +p _i ×Δn _i ×t _i /R _i ² and Δd≦0.

In the first invention, the first optical member is formed of a material with a positive refractive index temperature coefficient. The second optical member is formed of a material with a negative refractive index temperature coefficient. Both surfaces of the second optical member are formed to be flat. The light focusing position variation amount Δd is set to satisfy the above-mentioned condition.

This makes it possible to suppress fluctuations in the focusing position caused by the thermal lens effect with a relatively simple configuration.

Specifically, the refractive index temperature coefficient Δn is expressed as Δn = dn/dT, where n is the refractive index and T is the temperature. A material with a positive refractive index temperature coefficient is a material whose refractive index increases with increasing temperature, and for example, synthetic quartz can be used. A material with a negative refractive index temperature coefficient is a material whose refractive index decreases with increasing temperature, and for example, quartz can be used.

Here, by arranging the first optical member and the second optical member along the optical axis direction, the positive thermal lens effect generated in the first optical member can be cancelled out by the negative thermal lens effect generated in the second optical member. This makes it possible to suppress fluctuations in the focusing position of the laser light.

In addition, because the second optical member is a plate-shaped component with flat surfaces on both sides, there is no need to perform complex processing on the surface of the second optical member, which reduces component costs.

In addition, the light absorptance p _i , which is one of the parameters of the light-focusing position fluctuation amount Δd, increases when, for example, dirt adheres to an optical member. In other words, the light absorptance p _i tends to increase over time. Therefore, it is preferable to set the light-focusing position fluctuation amount Δd so that Δd≦0 in the initial state.

When the focusing position of the laser light has moved toward the optical element, the focusing position fluctuation amount Δd is considered to be positive.When the focusing position of the laser light has moved toward the workpiece, the focusing position fluctuation amount Δd is considered to be negative.

The second invention is the first invention, characterized in that the second optical member is made of quartz crystal.

In the second invention, the second optical member is made of quartz, so that the refractive index temperature coefficient of the second optical member is negative. Quartz is generally an expensive material, so by using a plate-shaped second optical member with flat surfaces on both sides, the processing costs of the parts can be reduced.

The third invention is characterized in that in the first or second invention, the number of the first optical members is greater than the number of the second optical members.

In the third invention, the number of first optical members is greater than the number of second optical members. Here, for example, synthetic quartz can be used as a material with a positive refractive index temperature coefficient. Also, for example, quartz can be used as a material with a negative refractive index temperature coefficient. Therefore, the number of second optical members made of quartz, which is an expensive material, can be reduced, thereby reducing costs.

The fourth invention is any one of the first to third inventions, characterized in that it is provided with a position adjustment unit that moves the second optical member in the optical axis direction.

In the fourth aspect of the present invention, the position adjustment unit moves the second optical member in the optical axis direction, thereby changing the focusing radius of the laser light on the surface of the second optical member. Specifically, the second optical member is moved in a direction in which the focusing radius R _i of the laser light on the surface of the second optical member becomes smaller.

In this way, by reducing the focusing radius R _i , which is one of the parameters of the focusing position variation Δd, the focusing position variation of the second optical member can be increased in the negative direction, whereby the sum of the focusing position variations calculated for each of the multiple optical members can be made a negative value.

The present invention makes it possible to suppress fluctuations in the focusing position caused by the thermal lens effect with a relatively simple configuration.

1 is a schematic diagram of a laser processing device according to an embodiment of the present invention. FIG. 11 is a diagram showing parameters of each optical member when the third shield glass is formed of the second optical member. 11 is a graph showing a difference in focusing position when laser light is emitted to a first optical member and a second optical member. FIG. FIG. 11 is a diagram showing parameters of each optical member when the second shield glass is formed of the second optical member in the present modification example 1. FIG. 11 is a diagram showing parameters of each optical member when the first shield glass is formed of the second optical member in the present modified example 2.

The following describes an embodiment of the present invention with reference to the drawings. Note that the following description of the preferred embodiment is essentially merely illustrative and is not intended to limit the present invention, its applications, or its uses.

As shown in FIG. 1, the laser processing device 10 includes a laser oscillator 11, a laser processing head 20, and a control unit 15.

The laser oscillator 11 outputs laser light L based on a command from the control unit 15. The laser oscillator 11 and the laser processing head 20 are connected by a transmission fiber 12. The laser light L is transmitted from the laser oscillator 11 to the laser processing head 20 via the transmission fiber 12. The laser processing head 20 emits the laser light L incident from the transmission fiber 12 to the workpiece W. The control unit 15 controls the operation of the laser oscillator 11 and the laser processing head 20. The control unit 15 has a function of controlling the moving speed of the laser processing head 20 as well as the start and stop of output of the laser light L, the output intensity of the laser light L, etc.

The laser processing head 20 is attached to a robot (not shown) and focuses the laser light L on the workpiece W based on commands from the control unit 15. The laser processing head 20 has multiple optical members aligned in the optical axis direction. The multiple optical members include a first shield glass 21, a collimator lens 22, a focus lens 23, a second shield glass 24, and a third shield glass 25.

Inside the laser processing head 20, a first shield glass 21, a collimator lens 22, a focus lens 23, a second shield glass 24, and a third shield glass 25 are arranged in this order from the upstream side in the emission direction of the laser light L.

The first shielding glass 21 is disposed on the output side of the transmission fiber 12. The first shielding glass 21 is composed of a plate-shaped member with flat surfaces on both sides. The first shielding glass 21 prevents dust from entering the inside of the laser processing head 20. The first shielding glass 21 is coated with an AR coating as an anti-reflection film.

The collimator lens 22 collimates the laser light L emitted from the output end of the transmission fiber 12. The collimator lens 22 is coated with an AR coating as an anti-reflection film.

The focus lens 23 focuses the laser light L collimated by the collimator lens 22. The focus lens 23 is coated with an AR coating as an anti-reflection film. The laser light L focused by the focus lens 23 passes through the second shield glass 24 and the third shield glass 25 and is emitted to the workpiece W.

The second shield glass 24 and the third shield glass 25 are disposed between the workpiece W and the focus lens 23. The second shield glass 24 and the third shield glass 25 protect the focus lens 23 so that fumes and spatters generated during laser processing of the workpiece W do not adhere to the focus lens 23. The second shield glass 24 and the third shield glass 25 are composed of plate-shaped members with flat surfaces on both sides. The second shield glass 24 and the third shield glass 25 are coated with an AR coating as an anti-reflection film.

The laser processing head 20 has a first position adjustment unit 31, a second position adjustment unit 32, and a third position adjustment unit 33. The first position adjustment unit 31 moves the first shield glass 21 in the optical axis direction. The second position adjustment unit 32 moves the second shield glass 24 in the optical axis direction. The third position adjustment unit 33 moves the third shield glass 25 in the optical axis direction.

The first position adjustment unit 31, the second position adjustment unit 32, and the third position adjustment unit 33 adjust the positions of the first shield glass 21, the second shield glass 24, and the third shield glass 25 based on instructions from the control unit 15.

However, when the laser light L has a high output (e.g., 4000 W), the optical components inside the laser processing head 20 heat up and distort, causing a thermal lens effect and resulting in a change in the focal position (so-called focal shift).

Therefore, in this embodiment, the materials of the multiple optical components arranged inside the laser processing head 20 are devised to suppress fluctuations in the focusing position due to the thermal lens effect.

The plurality of optical members include a first optical member and a second optical member. The first optical member is formed of a material with a positive refractive index temperature coefficient. The second optical member is formed of a material with a negative refractive index temperature coefficient.

Specifically, the refractive index temperature coefficient Δn is expressed as Δn = dn/dT, where n is the refractive index and T is the temperature. A material with a positive refractive index temperature coefficient is a material whose refractive index increases with increasing temperature, and for example, synthetic quartz can be used. A material with a negative refractive index temperature coefficient is a material whose refractive index decreases with increasing temperature, and for example, quartz can be used.

In the example shown in FIG. 1, the first shield glass 21, the collimator lens 22, the focus lens 23, and the second shield glass 24 are made up of the first optical member. The third shield glass 25 is made up of the second optical member.

The third shield glass 25 is made of quartz. Quartz is generally an expensive material, so by using a plate-shaped second optical member with flat surfaces on both sides, the processing costs of the component can be reduced.

In addition, in this embodiment, the first shield glass 21, the collimator lens 22, the focus lens 23, and the second shield glass 24 are made of the first optical member, and the third shield glass 25 is made of the second optical member. In other words, the number of first optical members is greater than the number of second optical members. Therefore, the number of second optical members made of quartz, which is an expensive material, can be reduced, thereby reducing costs.

In this embodiment, the optical members are assigned identification numbers i in order from the upstream side in the emission direction of the laser light L. Specifically, the identification number of the first shield glass 21 is "1", the identification number of the collimator lens 22 is "2", the identification number of the focus lens 23 is "3", the identification number of the second shield glass 24 is "4", and the identification number of the third shield glass 25 is "5".

Here, the identification number i of the optical member, the light absorptance p _i of the optical member, the refractive index temperature coefficient Δn _i of the optical member, the thickness t _i of the optical member, the focusing radius R _i of the laser light on the surface of the optical member, and the focusing position fluctuation amount Δd are set to satisfy the following formula (1): Note that the focusing radius R _i of the laser light L is the focusing radius on the upper surface of the optical member.

_Δd∝p1 × _Δn1 × _t1 / _R12 ⁺ ...+ _p1 × _Δn1 × _t1 / _Ri2 ^and Δd≦0... (1)
In this embodiment, five optical members (a first shield glass 21, a collimator lens 22, a focus lens 23, a second shield glass 24, and a third shield glass 25) are included. Therefore, formula (1) becomes formula (2) below.

Δd∝p1× _Δn1 × _t1 / _R12 + _p2 ^× _Δn2 × _t2 / _R22 + _p3 × _Δn3 ^{×t3/R32+p4×Δn4×t4/R42} ₊ ^p5 _{× Δn5 × t5 /} ^R52 _{and Δd ≦} ⁰ ( _{2 )}
2 is a diagram showing the parameters of the optical members when the third shield glass 25 is composed of the second optical member. As shown in FIG. 2, only the refractive index temperature coefficient Δn of the third shield glass 25 has a negative value.

Here, the state in which the focusing position of the laser light L has moved toward the optical member side is considered to have a positive focusing position fluctuation amount Δd. The state in which the focusing position of the laser light L has moved toward the workpiece W side is considered to have a negative focusing position fluctuation amount Δd.

2, the focal position fluctuation amount is a positive value in the first shield glass 21, the collimator lens 22, the focus lens 23, and the second shield glass 24. Therefore, in the first shield glass 21, the collimator lens 22, the focus lens 23, and the second shield glass 24, the focal position of the laser light L moves toward the optical component side due to the thermal lens effect.

On the other hand, the focal position fluctuation amount is a negative value in the third shield glass 25. Therefore, in the third shield glass 25, the focal position of the laser light L moves toward the workpiece W due to the thermal lens effect.

The sum of the light collection position fluctuations calculated for the first shield glass 21, the collimator lens 22, the focus lens 23, the second shield glass 24, and the third shield glass 25 is a negative value, which satisfies the condition Δd≦0.

Here, the light absorptance p _i , which is one of the parameters of the light-focusing position fluctuation amount Δd, increases when, for example, dirt adheres to an optical member. In other words, the light absorptance p _i tends to increase with time. Therefore, it is preferable to set the light-focusing position fluctuation amount Δd so that Δd≦0 in the initial state.

The light absorption rate varies depending on the material transmittance of the optical member, the coating applied to the optical member, dust and dirt attached to the optical member, etc. For example, when the amount of impurities contained in the material of the optical member is large, the material transmittance of the optical member decreases and the light absorption rate increases. In addition, when the transmittance, reflectance, or absorption rate of the AR coating applied to the optical member is low, the light absorption rate increases. In addition, when the amount of dust and dirt attached to the optical member is large, the light absorption rate increases. The higher the light absorption rate, the greater the amount of heat generated by the optical member heated by the laser light L.

In this embodiment, the second optical member is configured to have a small focusing radius R _i , which is one of the parameters of the focusing position fluctuation amount Δd. Specifically, the laser light L focused by the focus lens 23 is focused toward the workpiece W. Therefore, when the third shield glass 25 is moved toward the workpiece W by the third position adjustment unit 33, the focusing radius R ₅ of the laser light L on the surface of the third shield glass 25 becomes small.

As a result, by increasing the amount of light focusing position variation of the third shield glass 25 in the negative direction, the sum of the amounts of light focusing position variation calculated for each of the multiple optical components can be made a negative value.

Figure 3 is a graph showing the difference in focusing position when laser light is emitted to a first optical member and a second optical member. In the example shown in Figure 3, the difference in focusing position is compared when low-power (e.g., 500 W) laser light L and high-power (e.g., 4000 W) laser light L are emitted to multiple first optical members made of synthetic quartz and a second optical member made of quartz, each of which has a different light absorption rate.

As shown in Figure 3, in the first optical member made of synthetic quartz, the difference in the focusing position between low and high output of the laser light L is large, and it is clear that the influence of the thermal lens effect is large. On the other hand, in the second optical member made of quartz, the difference in the focusing position is small, and it is clear that the thermal lens effect is canceled.

As described above, with the laser processing head 20 according to this embodiment, the positive thermal lens effect generated in the first shield glass 21, the collimator lens 22, the focus lens 23, and the second shield glass 24 can be cancelled out by the negative thermal lens effect generated in the third shield glass 25. This makes it possible to suppress fluctuations in the focusing position of the laser light L.

--Modification 1--
4 , in the present modified example 1, the light collection position fluctuation amount is a positive value for the first shield glass 21, the collimator lens 22, the focus lens 23, and the third shield glass 25. In other words, the first shield glass 21, the collimator lens 22, the focus lens 23, and the third shield glass 25 are configured as the first optical member.

On the other hand, the second shield glass 24 has a negative light focusing position variation amount. In other words, the second shield glass 24 is composed of the second optical member.

The sum of the light collection position fluctuations calculated for the first shield glass 21, the collimator lens 22, the focus lens 23, the second shield glass 24, and the third shield glass 25 is a negative value, which satisfies the condition Δd≦0.

In addition, in this first modified example, in order to reduce the focused radius _R4 of the laser light L on the surface of the second shielding glass 24, the second shielding glass 24 can be moved toward the workpiece W by the second position adjustment unit 32.

As a result, by increasing the amount of light focusing position variation of the second shield glass 24 in the negative direction, the sum of the amounts of light focusing position variation calculated for each of the multiple optical components can be made a negative value.

--Modification 2--
5, in the present modified example 2, the collimator lens 22, the focus lens 23, the second shield glass 24, and the third shield glass 25 have positive values of the light collection position fluctuation amount. In other words, the collimator lens 22, the focus lens 23, the second shield glass 24, and the third shield glass 25 are configured as the first optical member.

On the other hand, the first shield glass 21 has a negative light focusing position variation amount. In other words, the first shield glass 21 is composed of the second optical member.

The sum of the light collection position fluctuations calculated for the first shield glass 21, the collimator lens 22, the focus lens 23, the second shield glass 24, and the third shield glass 25 is a negative value, which satisfies the condition Δd≦0.

Here, in the present modified example 2, the laser light L emitted from the transmission fiber 12 spreads toward the first shielding glass 21. Therefore, in order to reduce the focused radius _R1 of the laser light L on the surface of the first shielding glass 21, the first shielding glass 21 may be moved toward the emission end of the transmission fiber 12 by the first position adjustment unit 31.

As a result, by increasing the amount of light focusing position variation of the first shield glass 21 in the negative direction, the sum of the amounts of light focusing position variation calculated for each of the multiple optical components can be made a negative value.

As described above, the present invention has a relatively simple configuration and is highly practical in that it can suppress fluctuations in the focusing position caused by the thermal lens effect, making it extremely useful and highly applicable in industry.

10 Laser processing device 12 Transmission fiber
20 Laser processing head
21 First shield glass (first optical member)
22 Collimator lens (first optical member)
23 Focus lens (first optical member)
24 Second shield glass (first optical member)
25 Third shield glass (second optical member)
31 First position adjustment unit 32 Second position adjustment unit 33 Third position adjustment unit L Laser light W Workpiece

Claims (4)

A laser processing head that outputs laser light incident from a transmission fiber to a workpiece,
a plurality of optical members arranged on an output side of the transmission fiber and aligned along an optical axis;
the plurality of optical members include a first optical member formed of a material having a positive refractive index temperature coefficient and a second optical member formed of a material having a negative refractive index temperature coefficient;
Among the plurality of optical members installed inside the laser processing head, the first optical member is installed as the most downstream optical member,
The identification number i of the optical member, the light absorptance p _i of the optical member, the refractive index temperature coefficient Δn _i of the optical member, the thickness t _i of the optical member, the focusing radius R _i of the laser light on the surface of the optical member, and the focusing position fluctuation amount Δd in the initial state are expressed as
Δd ∝ p ₁ × Δn ₁ × t ₁ / R ₁ ² + ... + p _i × Δn _i × t _i / R _i ² and Δd < 0
A laser processing head characterized by satisfying the above conditions. In claim 1,
A laser processing head, wherein the second optical member is formed of quartz crystal. In claim 1 or 2,
A laser processing head, characterized in that the number of the first optical members is greater than the number of the second optical members. In any one of claims 1 to 3,
A laser processing head comprising a position adjustment unit that moves the second optical member in an optical axis direction.

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